Audiophonics HPA-S400ET Class D Purifi amp

[Fledermaus]

It depends on the DAC specs, best if you aim for robust output voltage and low output impedance, naturally. Works fine here with 50 Ohm / 20 dBu output DAC cards : https://www.xilica.com/products/solaro-xc-slo/

 

[WireWoundResistor]

I am using a Topping D70S directly connected to the Audiophonics in bypass mode. I read the Topping has an output impedance of around 200 ohms, so quite lower that the input impedance of the amp. I have never compared the sound with or without the buffer, but i have read around that if the input impedance of the amp is more than 10X the output impedance of the source it's ok. Am i missing something? Are you worried since your source having a higher output impedience?

10:1 is the bare minimum, I like 100:1 better, especially driving a balanced connection with a small DAC power supply. My E70 (100ohms or so) sounds significantly different when the buffer is bypassed (slightly less top end and less punchy) and even with a simple resistive load in between it sounds better again. It always depends on the output stage of the DAC and the Topping seems to lack the current to drive the Purifi modules directly or whatever. I know it sounds stupid and it shouldn't be that way, btw. With the buffer in I have way to much gain, and have to attenuate too much, but it's still the better solution at the moment. I'm gonna change the resistors around the OP amp so I can have a unity gain buffer as soon as I get around to it. All other manufacturers did that from the get go, as far as I'm aware of. Why advertise a buffer board with three gain settings if one of them is just the bare ass module input.

 

[BR52]

10:1 is the bare minimum, I like 100:1 better, especially driving a balanced connection with a small DAC power supply. My E70 (100ohms or so) sounds significantly different when the buffer is bypassed (slightly less top end and less punchy) and even with a simple resistive load in between it sounds better again. It always depends on the output stage of the DAC and the Topping seems to lack the current to drive the Purifi modules directly or whatever. I know it sounds stupid and it shouldn't be that way, btw. With the buffer in I have way to much gain, and have to attenuate too much, but it's still the better solution at the moment. I'm gonna change the resistors around the OP amp so I can have a unity gain buffer as soon as I get around to it. All other manufacturers did that from the get go, as far as I'm aware of. Why advertise a buffer board with three gain settings if one of them is just the bare ass module input.

Could you prove it with measurements, or is your statement only coming from a level difference? 4.4k and 100 Ohms the ratio is 44 I guesss, and the only ca 1mA max. driving current every OP-amp can handle easily. I could see the effect from your post with a DAC with much higher output impedance (passive filtering) as well, a KOhm or so.

 

[JohnnyNG]

10:1 is the bare minimum, I like 100:1 better, especially driving a balanced connection with a small DAC power supply. My E70 (100ohms or so) sounds significantly different when the buffer is bypassed (slightly less top end and less punchy) and even with a simple resistive load in between it sounds better again. It always depends on the output stage of the DAC and the Topping seems to lack the current to drive the Purifi modules directly or whatever. I know it sounds stupid and it shouldn't be that way, btw.

I've experienced some weirdness in this area and cannot explain (or prove!) it. My Topping Pre90 (40 ohm XLR output Z, >10v clean output) ) should have no problem driving my Audiophonics MPA-M400ET monos in bypass (4.4 kΩ) yet the combo sounds noticeably worse than buffered at 94kΩ. In bypass the sound seems compressed and, well, colorless. I'm using 25' runs of Canare L-4E6S but that shouldn't matter I think?

 

[WireWoundResistor]

Could you prove it with measurements, or is your statement only coming from a level difference? 4.4k and 100 Ohms the ratio is 44 I guesss, and the only ca 1mA max. driving current every OP-amp can handle easily. I could see the effect from your post with a DAC with much higher output impedance (passive filtering) as well, a KOhm or so.

I couldn't measure it so far, but I'll try to measure it at the speaker output as soon as I got the setup to do that. I know, trained ears and stuff means nothing here (audio engineer for 15 years) but it just sound noticeably duller to my ears. I usually don't trust my ears, but I went back and forth a couple of times, because I like the gain staging more without the buffer, and the feeling remains. I also tried quick A/B switching (DAC output) with a different amp, the impression is the same. Indistinguishable with the buffer in, rolled off in comparison with the buffer on bypass. I tried with an active DI box (unity gain buffer) in between and it also got better. Maybe it's something else, not the impedance, but it sure has all the symptoms. Believe me, I also did the math first and thought it impossible. My cables between DAC and amp are 50cm long, so even with that low of an input impedance, capacitance shouldn't be an issue either.